An optical proximity fuze is a device associated with an explosive projectile which is capable of detonating the projectile when it is in proximity to a target. The fuze generally comprises a source of radiation which directs a narrow beam of radiation toward a target, and a receiver or detector which responds to radiation reflected by the target back to the fuze. The detector provides an output signal in response to the radiation incident thereto. When this output signal reaches a threshold level, the detonator may be activated using such signal.
Due to physical and optical limitations, as will be discussed more fully below, radiation sufficient to generate an output signal at the detector above the level needed to detonate the explosive is incident to the detector only within a relatively narrow range of distances to the target. In most instances, the range in which the fuze will respond to incident radiation is deliberately narrowed so as to desensitize the optical fuze to aerosols, such as fog or haze. If the fuze is not desensitized, these aerosols may provide spurious reflective signals tending to activate the fuze at a time when it is not desirable to do so.
A common method utilized to desensitize the fuze to aerosols comprises placing a field stop, or opaque mask, in front of the detector. An aperture in the field stop is selectively positioned so as to allow only a particular portion of the reflected radiation to reach the detector. This permits the fuze to function at a selected range while preventing spurious short range reflections from aerosols from reaching the detector. While this is a desirable result, it is accompanied by the undesirable effect that the fuze is rendered non-responsive to reflections of radiation from the desired target at close range. Merely enlarging the aperature would render the fuze responsive to the target at close range, but would again make it sensitive to the spurious reflections from the aerosols.
Accordingly, it is an object of this invention to provide means to overcome the disadvantages associated with the prior art devices described above.
It is an object of this invention to improve and enlarge the range function of optical fuzes without making the fuzes unduly sensitive to air-borne particles and aerosols.
It is an object of this invention to provide means to shape the range response function of an optical fuze in any manner deemed to be desirable.